SUBPROJECT - B1
A global model of redox-dependent biogeochemical cycles
A main focus is the further development and calibration of the central biogeochemical SFB 754 model of pelagic and benthic redox-dependent biogeochemical processes. SFB 754 field studies addressing impacts of different inorganic and organic nutrient ratios on biological production and export fluxes (B2, B9), redox-sensitive pelagic remineralisation (B4, B8, B9) and benthic-pelagic coupling of N, P and Fe (B5, B6, B7, B10) will be examined in a coherent regional to global context. To this extent seasonally cycling global circulation fields from the ECCO project will be employed in the computationally efficient Transport Matrix Method that allows simulations over thousands of years per day and thereby enables a full exploration of feedbacks between local processes and global biogeochemical tracer distributions. Model results will be compared with, and model parameterisations and parameters will be calibrated against, observed regional and global biogeochemical tracer distributions and rate estimates in the water column and the sediments.
A novel focus of the third phase will be the explicit consideration of non-steady state conditions and the development of model formulations more adequate for describing biogeochemical responses to temporally varying environmental conditions, with a special focus on the region off Peru. This is particularly relevant with respect to remineralisation processes in the water column (B9) as well as benthic-pelagic processes and their responses to variable redox conditions and particle fluxes. While the parameterizations of benthic- pelagic exchanges via steady-state transfer functions applied in Phase II implicitly assumed non-specified, infinite benthic reservoirs (of carbon, nitrogen, phosphorus) and instantaneous response to changes in environmental conditions, an explicit sediment module will be developed in the third Phase of the SFB 754. This will allow us to account for finite sedimentary tracer inventories, realistic organic matter degradation kinetics and finite response times of benthic processes to changes occurring in the water column. These are of particular relevance in the highly dynamic Peruvian upwelling region and its representation in the regional high-resolution ROMS model will be developed jointly with A2. The impact of transient benthic feedbacks will also be assessed in global simulations performed in A1, A2 and A7 and compared against results of the steady-state transfer functions developed during Phase II of the SFB 754 .
Dale, A.W., S. Sommer, U. Lomnitz, I. Montes, T. Treude, J. Gier, C. Hensen, M. Dengler, K. Stolpovsky, L.D. Bryant and K. Wallmann (2014) Organic carbon production, mineralization and preservation on the Peruvian margin. Biogeosciences, 12, 1537-1559, doi: 10.5194/bg-12-1537-2015
Dale, A.W., V.J. Bertics, T. Treude, S. Sommer and K. Wallmann (2013) Modeling benthic– pelagic nutrient exchange processes and porewater distributions in a seasonally hypoxic sediment: evidence for massive phosphate release by Beggiatoa? Biogeosciences, 10, 629- 651, doi: 10.5194/bg-10-629-2013
Bohlen, L., A.W. Dale and K. Wallmann (2012) Simple transfer functions for calculating benthic fixed nitrogen losses and C:N:P regeneration ratios in global biogeochemical models. Glob. Biogeochem. Cy., 26, GB3029, doi: 10.1029/2011GB004198
Kalvelage, T., G. Lavik, P. Lam, S. Contreras, L. Arteaga, C.R. Löscher, A. Oschlies, A. Paulmier, L. Stramma and M.M.M. Kuypers (2013) Nitrogen cycling driven by organic matter export in the South Pacific oxygen minimum zone. Nat. Geosci., 6, 228-234, doi: 10.1038/ngeo1739
Kriest, I. and A. Oschlies (2013) Swept under the carpet: organic matter burial decreases global ocean biogeochemical model sensitivity to remineralization length scale. Biogeosciences, 10, 8401-8422, doi: 10.5194/bg-10-8401-2013
Kriest, I., A. Oschlies and S. Khatiwala, (2012) Sensitivity analysis of simple global marine biogeochemical models. Glob. Biogeochem. Cy., 26, GB2029, doi: 10.1029/2011GB004072
Landolfi, A., H. Dietze, W. Koeve and A. Oschlies (2013) Overlooked runaway feedback in the marine nitrogen cycle: the vicious cycle. Biogeosciences, 10, 1351-1363, doi: 10.5194/bg-10- 1351-2013
Montes, I., B. Dewitte, E. Gutknecht, A. Paulmier, I. Dadou, A. Oschlies and V. Garçon (2014) High-resolution modeling of the Eastern Tropical Pacific oxygen minimum zone: Sensitivity to the tropical oceanic circulation. J. Geophys. Res. Oceans, 119, 5515-5532. doi: 10.1002/ 2014JC009858
Somes, C.J., A. Oschlies and A. Schmittner (2013) Isotopic constraints on the pre-industrial oceanic nitrogen budget. Biogeosciences, 10: 5889-5910, doi: 10.5194/bg-10-5889-2013
Stramma, L., A. Oschlies and Schmidtko, S. (2012) Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr. Biogeosciences, 9, 4045-4057. doi: 10.5194/bg-9-4045-2012